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Causes
By Mayo Clinic staff
The complex process of sight begins when light reflecting off an object enters the clear outer portion of your eyeball (cornea) and passes through the lens, which brings the light into focus on the nerve cell layer of your eye (retina). When light hits the retina, electrical impulses are generated and carried along the optic nerve to your brain, where the impulses are converted into visual information.
The optic nerve is a bundle of nerve fibers covered by a fatty insulated material called myelin, which helps electrical impulses travel quickly along the nerve. Optic neuritis in young adults is believed to most commonly develop when the immune system attacks myelin covering the optic nerve, resulting in inflammation and damage. It's not certain what causes your immune system to attack its own tissue. The following two autoimmune conditions are often associated with optic neuritis:
- Multiple sclerosis. Multiple sclerosis is a disease in which your autoimmune system attacks the myelin sheath covering nerve fibers in your brain and spinal cord. In one long-term study of people with optic neuritis, the risk of developing multiple sclerosis following one episode of optic neuritis was 50 percent after 15 years. The evidence of brain lesions on MRI images increased the risk. People with optic neuritis and abnormal MRI scans were three times more likely to develop multiple sclerosis compared with those who had normal MRI scans.
- Neuromyelitis optica. Another autoimmune condition that may cause optic neuritis is neuromyelitis optica. In this condition, inflammation occurs in the optic nerve and spinal cord. Neuromyelitis optica isn't the same as multiple sclerosis, because neuromyelitis optica doesn't cause damage to the nerves in the brain as often as multiple sclerosis does. Optic neuritis arising from neuromyelitis optica tends to be more severe than optic neuritis associated with multiple sclerosis.
Other causes of optic neuritis include:
- Infections. Bacterial infections, including Lyme disease, cat scratch fever and syphilis, or viruses such as HIV, hepatitis B and herpes can cause optic neuritis. In addition, some infections may lead to a type of optic neuritis, called neuroretinitis, which isn't believed to be associated with the risk of developing multiple sclerosis.
- Cranial arteritis. This is an inflammation of the lining of the arteries in your head. Inflamed cranial arteries can block blood flow to your eyes and brain, which may cause permanent vision loss or a stroke. Cranial arteritis is most likely to occur in adults ages 70 to 80.
- Diabetes. Diabetes is a condition in which your body can't make or properly use insulin, a hormone that regulates the amount of sugar in your blood. People with diabetes are at an increased risk of developing disorders of the optic nerve.
- Drugs. Some drugs have been associated with the development of optic neuritis. One of these drugs is ethambutol (Myambutol), which is used to treat tuberculosis.
Radiation therapy to your head is an uncommon cause of optic neuritis. In addition, any process resulting in inflammation or compression of the optic nerve, including tumors, nutritional deficiencies or toxins, can interfere with the nerve's ability to conduct electrical impulses. This may cause vision loss and other symptoms that may mimic optic neuritis.
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